HELP! Noise on LFE pre-outs (Onkyo)

[mirage_man]

EDIT: Problem solved. See post#9 and #22

Here's my situation. I use an Onkyo TX-NR809 as a pre/pro feeding an ATI-1505 for LCR+LR duty and an ATI 1502 to power a dual 15" IB. The signal feeding the 1505 seems to be fine with no real noise. However I get a substantial hum/noise coming from the sub-woofers if I increase the sub signal in the Onks level menu to anything near 0DB which I assume is just increasing the line voltage output. The hum does increase and decrease some with master volume adjustment but disappears completely when the unit is muted. If I am playing a CD near 0DB (volume setting) and pause the track the hum is VERY loud but while playing at that volume it is of course not audible.

The hum is not present when the interconnects are disconnected. Based on what I've tried so far I have assume it's a signal issue and not a ground loop although I've gone through every usual exercise in isolating the problem as just that (trust me ).

The problem gets worse because I now plan to use a pro QSC DCA amp to drive not only the IB sub but also a sealed Tempest that will be located within feet of the listening position. I am probably like several here, quite OCD when it comes to noise issues and this is really driving me nuts. I spent some time today speaking with a tech at QSC and he thinks it's an issue with the Onkyo. I also spoke to a local repair tech that said it sounded like a ground issue inside the Onk. I tested the grounds on the Sub outputs and they tested ohmed out just like all the others.

Has anyone else experienced anything like this? I'm at a loss. Could it be that the LFE signal from the Onk is just noisy as hell or might it be that there truly is something amiss in the circuitry?

When I have the level set to say -9db and powering the subs with the ATI there's very little hum although still there. When I use the QSC amp I need more voltage to drive it to the same level as the ATI. Yes, I can turn the gains up on the QSC but it just increases the hum.

ARRGH!

Front stage before flooring..

[DE Focht]

Re: HELP! Noise on LFE pre-outs (Onkyo)

Here's my situation. I use an Onkyo TX-NR809 as a pre/pro feeding an ATI-1505 for LCR+LR duty and an ATI 1502 to power a dual 15" IB. The signal feeding the 1505 seems to be fine with no real noise. However I get a substantial hum/noise coming from the sub-woofers if I increase the sub signal in the Onks level menu to anything near 0DB which I assume is just increasing the line voltage output. The hum does increase and decrease some with master volume adjustment but disappears completely when the unit is muted. If I am playing a CD near 0DB (volume setting) and pause the track the hum is VERY loud but while playing at that volume it is of course not audible.

The hum is not present when the interconnects are disconnected. Based on what I've tried so far I have assume it's a signal issue and not a ground loop although I've gone through every usual exercise in isolating the problem as just that (trust me ).

The problem gets worse because I now plan to use a pro QSC DCA amp to drive not only the IB sub but also a sealed Tempest that will be located within feet of the listening position. I am probably like several here, quite OCD when it comes to noise issues and this is really driving me nuts. I spent some time today speaking with a tech at QSC and he thinks it's an issue with the Onkyo. I also spoke to a local repair tech that said it sounded like a ground issue inside the Onk. I tested the grounds on the Sub outputs and they tested ohmed out just like all the others.

Has anyone else experienced anything like this? I'm at a loss. Could it be that the LFE signal from the Onk is just noisy as hell or might it be that there truly is something amiss in the circuitry?

When I have the level set to say -9db and powering the subs with the ATI there's very little hum although still there. When I use the QSC amp I need more voltage to drive it to the same level as the ATI. Yes, I can turn the gains up on the QSC but it just increases the hum.

ARRGH!

Front stage before flooring..

What happens when you disconnect the service cable from the cable box?

[mirage_man]

Re: HELP! Noise on LFE pre-outs (Onkyo)

What happens when you disconnect the service cable from the cable box?

Same thing. I've tried all the usual remedies for ground loops.

I've removed all cables (including cable tv feed) and components except for the the bluray player to use as a source to check for noise when paused with an active signal. There must be a signal present to hear the hum or the Onk mutes the signal and the hum goes away.
Lifting the ground on the amp with cheater plug. The receiver does not use a ground on its power chord.
Different cables.
All components are plugged into the same Monster Power surge protector.
Tried removing said MP strip and plugging everything directly into the same outlet.

No matter what I do I still get the noise whether it's the ATI amp or QSC amps but it seems only from the sub out.

[Psycoacoustics]

Re: HELP! Noise on LFE pre-outs (Onkyo)

Is it possible you broke the ground connection inside the receiver while plugging and unplugging the sub cable? You'd have to open it up to check. I've seen this a couple of time when the cables are real tight.

I feel for ya! Good luck, Mark

[mirage_man]

Re: HELP! Noise on LFE pre-outs (Onkyo)

Is it possible you broke the ground connection inside the receiver while plugging and unplugging the sub cable? You'd have to open it up to check. I've seen this a couple of time when the cables are real tight.

I feel for ya! Good luck, Mark

I checked the grounds of all the pre-outs with my multi-meter and they all ohm out to ground with the same reading.

Would a bad capacitor in the sub out circuit cause hum or noise? I did have an issue with the 2 channel ATI where a trace on one of the channels output board burned up and had to be repaired. Could it have back fed voltage over the RCA's into the sub out and damaged something?

[Stevers]

Re: HELP! Noise on LFE pre-outs (Onkyo)

It sounds like it is your Onkyo. However, if you disconnect the sub-out from your Onkyo to the ATI and use instead, the LF or RF to feed the ATI (and change your front speaker config in the Onkyo to full) is the hum still present? I think that would isolate your sub-outs in the Onkyo.

Are there any A/C lines crossing/near the sub connects?

[mirage_man]

Re: HELP! Noise on LFE pre-outs (Onkyo)

It sounds like it is your Onkyo. However, if you disconnect the sub-out from your Onkyo to the ATI and use instead, the LF or RF to feed the ATI (and change your front speaker config in the Onkyo to full) is the hum still present? I think that would isolate your sub-outs in the Onkyo.

Are there any A/C lines crossing/near the sub connects?

I will try that.

No AC lines. I've been able to reproduce the same noise with my sealed sub across the room at the listening position with an entirely different speaker cable and amp.

[john trials]

Re: HELP! Noise on LFE pre-outs (Onkyo)

A bit off topic, but since you posted a photo...

Very nice looking room and audio system! What are the alcove areas to the left and right used for? Is that access to behind the shelving where you have the audio components?

[mirage_man]

Re: HELP! Noise on LFE pre-outs (Onkyo)

Well I feel like a dumbass :rolleyes: But I am a very happy camper at the same time. :D

I traced it down to a ground loop after all. I had the tv plugged into a different circuit in a recessed wall box behind the tv. The hum went away when I unplugged the tv from that outlet and the HDMI cord. I ran an extension cord for the tv over to the monster power line conditioner/surge protector and no more hum, DOH! Waht a dope. I though I had tried this already without success.

No the question is how to remedy this? Since the power strip is not right behind the tv how does one go about tying the two together to eliminate the loop?

[Psycoacoustics]

Re: HELP! Noise on LFE pre-outs (Onkyo)

If the outlet you plug the tv into is on the same circuit the Monster Power is plugged into,,,,, than I'd go to Guitar Center and buy a Hum-X to plug the tv into. Otherwise, wire the two outlets to the same circuit. That could be a crap shoot too though.

My cable box is plugged into a Hum-x for pretty much the exact same problem.

Good luck! Mark

[mirage_man]

Re: HELP! Noise on LFE pre-outs (Onkyo)

A bit off topic, but since you posted a photo...

Very nice looking room and audio system! What are the alcove areas to the left and right used for? Is that access to behind the shelving where you have the audio components?

Thanks. It's been a long road remodeling this room (did all the work myself). The alcoves with eventually have built in shelves for artwork and such. The recessed lights will shine down on sculptures or something interesting.

Access to the rear of the components is from the room behind the wall.

Started out like this!

[mirage_man]

Re: HELP! Noise on LFE pre-outs (Onkyo)

If the outlet you plug the tv into is on the same circuit the Monster Power is plugged into,,,,, than I'd go to Guitar Center and buy a Hum-X to plug the tv into. Otherwise, wire the two outlets to the same circuit. That could be a crap shoot too though.

My cable box is plugged into a Hum-x for pretty much the exact same problem.

Good luck! Mark

Funny thing is the cable is not the issue, it's the tv itself. The hum was present regardless whether the cable feed was connected or not. I know that's the most common culprit. If you look at the last picture I posted above you will see I already have a isolation filter on the cable feed line .

Oh, and by the way, the wiring in this pick is only temporary until I have time to make custom cables and tidy everything up. Still not quite done with the room itself but I had to make it livable with the system playing :D .

The circuit the tv is plugged into is separate from the audio gear. I did this intentionally to reduce the draw on that circuit since I have a plasma which draws a decent amount of juice. Loading one 20 amp circuit with all my amps and gear along with the tv didn't seem like a good idea. I also thought, apparently erroneously that having them separate would reduce the risk of audio noise being introduced by the tv's transformer being on the same circuit.

I can't tie the two circuits together at the panel because it would put too much of a load on it. I have other lights and such on the same circuit as the tv's.

[Psycoacoustics]

Re: HELP! Noise on LFE pre-outs (Onkyo)

Any dimmers on those lights?

[mirage_man]

Re: HELP! Noise on LFE pre-outs (Onkyo)

Any dimmers on those lights?

Yes. A lutron LED dimmer switch.

[mirage_man]

Re: HELP! Noise on LFE pre-outs (Onkyo)

What if I figure a way to jump a wire from the ground terminal on the TV outlet over to the ground terminal on the outlet where the audio gear is plugged in? It would be a real challenge since the drywall is already up but would that work?